This invention relates to the sphere of growing corundum monocrystals (leucosapphire).
A method for growing corundum monocrystals from a melt by pulling on inoculation seed (Chokhralsky technique) is known in the present art and wherein, a blend or stock is charged into a container and heated until rendering same into a melt by using the energy of a H.F. electric field, and whereupon an inoculant is placed into the melt and a single crystal is pulled thereinto.
The method of a single-crystal growth process is run in an iridium container within an inert gas atmosphere.
A disadvantage inherent in the said technique of growing single crystals of corundum resides in the use of an iridium-made container. Such containers are critical, costly and short-lived which results in high production cost of the corundum crystals grown therein.
Another disadvantage of the known method lies in the difficulty of gowing large-sized monocrystals of corundum (200.times.100.times.15 mm and over). In said method, as a rule, only 50 percent the total volume of the melt is used for the growth of monocrystals. Therefore, for growing the large sized corundum monocrystals it is necessary to use either big iridium crucibles or to a complicated auxiliary equipment and apparatus which requires precision charging of the container with the blend as fast as the crystal is pulled from the melt.
Besides, the abovesaid growth technique for corundum monocrystals also requires an intricate apparatus for controlling the inert-gas shielding atmosphere. An insert gas is indispensable in the process in order to preclude an intense evaporation of the iridium container. However, some excess inert gas pressure of the gas hampers evaporation of the melt of not only this iridium but also a number of the impurities which affects the chemical purity of the stock blend.
Apart from the above-discussed disadvantages of the aforesaid method, the use of the energy of a H.F. field for heating the container to a great extent hinders the formation of the required temperature fields within the growth some of the monocrystal, also affecting the quality thereof.